Grinding wheel

ABSTRACT

The invention relates to a grinding wheel for the material-removing machining of at least one workpiece, preferably a grinding wheel for the simultaneous material-removing machining of at least two flat workpieces, wherein the grinding wheel is provided with a base body and a grinding layer arranged thereon for the grinding machining of the at least one workpiece, and wherein the grinding layer comprises a plurality of surface segments, wherein, in each case, a plurality of surface segments is provided both in the circumferential direction and in the radial direction. In order to specify a grinding wheel with which both harder and softer workpieces can be machined with good machining results and good wear behavior of the grinding wheel, the grinding layer should comprise at least two different types of surface segments with different degrees of hardness.

The invention relates to a grinding wheel for the material-removingmachining of at least one workpiece, preferably a grinding wheel for thesimultaneous material-removing machining of at least two flatworkpieces, wherein the grinding wheel is provided with a base body anda grinding layer arranged thereon for the grinding machining of the atleast one workpiece, and wherein the grinding layer comprises aplurality of surface segments, wherein, in each case, a plurality ofsurface segments is provided both in the circumferential direction andin the radial direction.

Such grinding wheels, in which the hardness of the surface segments ismatched to the respective application, are known from practice. In thisrespect, grinding wheels with harder surface segments for machining hardworkpieces, such as hardened steel, and grinding wheels with less hardsurface segments for machining less hard workpieces, such as copper, areknown.

In this application, “hardness” is used as the term for the modulus ofelasticity of the material, since the modulus of elasticity correlateswith the “hardness” (in the linguistic sense) of a grinding tool as ameasure of wear resistance. In this respect, the term “harder” isunderstood as a higher modulus of elasticity value and “less hard” or“softer” designates a lower modulus of elasticity value.

For the application relevant in this case, the modulus of elasticityshould be in the range of 40 GPa to 120 GPa, preferably 70 GPa to 105GPa.

In this respect, the modulus of elasticity for determining such valuesis determined using the resonance method, also known as acoustichardness testing. The elasticity modulus is determined in accordancewith DIN EN 843-2 (2006). The natural frequency of a test specimen isused in conjunction with sample dimensions and additional materialproperties (density) to calculate the modulus of elasticity. For thispurpose, the test specimen is brought into direct contact with a piezotransducer and continuously vibrated over a fixed frequency spectrum (atmost between 100 Hz and 100 kHz) [DIN EN 843-2 (2006)]. If theexcitation frequency corresponds to the fundamental frequency of thesample, resonance oscillation with maximum amplitude occurs. In thismanner, the natural frequency can be determined with the assistance ofanother piezoelectric sensor. The natural frequency is used for asubsequent calculation of the modulus of elasticity according to DIN EN843-2 (2006).

The measuring instrument used for this can, for example, be a ZVUK 130(supplier: ABRASIV, a.s., Pod Borkem 312, 293 01 Mlada Boleslav, CzechRepublic).

A disadvantage of the previously known grinding wheels is that, inpractice, situations arise in which, in a short time sequence, hardworkpieces and less hard workpieces have to be machined in alternation.This means that either different grinding wheels are used and, in thisrespect, the grinding machine used has to be modified accordingly. Inaddition to the increased financial expenses for holding the variousgrinding wheels available, the set-up times also lead to a reduceduseful life of the grinding machine, which also constitutes a financialimpairment.

If, instead, only one grinding wheel with a higher hardness is used formachining hard and less hard workpieces, it must be sufficiently hardfor machining the hard workpieces. In practice, however, when machiningless hard workpieces with such a grinding wheel, material inclusionsoccur increasingly on the surface segments of the grinding wheel, whichlead to an adverse effect on the grinding pattern. The materialinclusions are workpiece dust, for example metallic particles, whichadhere to the surface segments. A hard grinding wheel tends to formplateaus when the surface segments are worn; this leads to increasedfrictional heat in certain areas, which can cause particles to adhere tothe surface segments.

The object of the invention is to avoid the aforementioned disadvantagesand to specify a grinding wheel with which both harder and softerworkpieces can be machined with good machining results and good wearbehavior of the grinding wheel.

This object is achieved with a generic grinding wheel in that thegrinding layer comprises at least two different types of surfacesegments, which have different degrees of hardness. The differentsurface segments of the grinding wheel are of the same height when thegrinding wheel is unused, and remain at the same height as a result ofuniform wear of the surface segments. This means that two differentgrinding wheels or grinding wheel sets (with a simultaneous double-sidedmachining of the workpieces) are not required and the corresponding lossof time due to conversion of the grinding machine is eliminated. At thesame time, the performance in terms of removal is virtually unchanged,with only a slight increase in wear on the grinding wheel. The roughnessof the workpiece surface produced, which is also negatively affected byscratches from material inclusions in the grinding layer of the grindingwheel, is improved compared to a grinding wheel that only has surfacesegments with the high degree of hardness.

Preferably, at least a first group of harder surface segments and asecond group of softer surface segments can be provided. The hardness ofthe respective surface segments is influenced by the bond (usually bymeans of glass frit) and the type and proportion of the grain size (forexample, diamond or CBN), as well as by the proportion of the binder(for example, glass frit) and the proportion of a secondary grain, forexample aluminum oxide.

In this respect, the ratios of the differently hard surface segments toeach other can be arbitrary; for example, a distribution of hardersurface segments/softer surface segments of 20%/80% up to 80%/20% ispossible. Preferably, the distribution can amount to 30%/70% up to70%/30%. With more than 2 different hard types of surface segments,other divisions are also possible. Advantageously, the proportion ofharder surface segments can always be higher than the proportion ofsofter surface segments or vice versa.

According to the invention, the harder surface segments can have ahardness that is at least 5% harder than the hardness of the softersurface segments, preferably 10% to 20% harder than the hardness of thesofter surface segments.

Advantageously, at least some of the surface segments can be eithercircular or annular, or even hexagonal. Thus, the entirety of thesurface segments can form a total surface without a high proportion offree spaces between the surface segments.

In this respect, at least some of the surface segments can also bequadrangular with straight and/or curved side edges.

Preferably, at least two adjacent surface segments may be separated fromone another by a recessed area, for example in the form of a groove. Therecessed areas can also be used, for example, for the intake/removal ofcoolants and/or lubricants.

Viewed in the radial direction, at least one recessed area can extendover the entire radial extension of the grinding wheel and/or, viewed inthe radial direction, at least one recessed area can extend only over apartial area of the radial extension of the grinding wheel.

Alternatively, adjacent surface segments can be arranged directlyadjacently to each other (that is, “butt jointed”).

Furthermore, at least one recessed area can extend radially or in theform of an involute.

In a preferred exemplary embodiment of the invention, at least onerecessed area, preferably each recessed area, may be filled, at leastpartially, preferably completely, with a filling material, such as epoxyresin.

According to the invention, at least one recessed area, preferably eachrecessed area, may have a width of at least 1 mm, preferably 3 mm to 5mm.

Preferably, at least one harder surface segment and at least one softersurface segment can be provided at each radial position of the grindingwheel when viewed in the circumferential direction. This ensures thatthe desired machining result can be achieved with every radial positionof the grinding wheel. At any radial position of the grinding wheel whenviewed in the circumferential direction, the proportion occupied by theat least one harder surface segment and the proportion occupied by theat least one softer surface segment can advantageously be of approximateuniform size.

Advantageously, the material thickness of the surface segments can be atleast 3 mm, preferably 5 mm to 10 mm. In this respect, the depth of therecessed areas can correspond to the material thickness of the surfacesegments, or at least be slightly smaller.

The invention also relates to a grinding wheel set with two grindingwheels for the simultaneous material-removing machining of both sides ofat least two flat workpieces.

An additional object of the invention in this respect is to avoid thedisadvantages mentioned above and to specify a grinding wheel set withwhich both harder and softer workpieces can be machined with goodmachining results and good wear behavior of the grinding wheels of thegrinding wheel set.

This object is achieved with a generic grinding wheel set in that atleast one grinding wheel is a grinding wheel according to the invention,and preferably each of the grinding wheels is a grinding wheel accordingto the invention.

In the following, an exemplary embodiment of the invention shown in thedrawing is explained. The only figure shows a grinding wheel 1, whichhas a base body and a grinding layer arranged thereon for the grindingmachining of at least one workpiece not shown in the drawing.

The grinding layer comprises a plurality of surface segments 2, 3, whichare hexagonal in the exemplary embodiment shown, wherein, in each case,a plurality of surface segments is provided both in the circumferentialdirection and in the radial direction.

In each case, adjacent surface segments 2, 3 are separated from eachother by a recessed area 4 in the form of a groove. In this respect, therecessed area 4, viewed in the radial direction, extends over the entireradial extension of the grinding wheel 1.

The grinding wheel 1 also comprises a base body 5, to which the surfacesegments 2, 3 are preferably attached by gluing.

The surface elements 2, 3 of the grinding layer are divided into twodifferent types of surface segments 2, 3, which have different degreesof hardness, and comprise a first group of harder surface segments 2 anda second group of softer surface segments 3.

1. Grinding wheel (1) for the material-removing machining of at leastone workpiece, preferably a grinding wheel (1) for the simultaneousmaterial-removing machining of at least two flat workpieces, wherein thegrinding wheel (1) is provided with a base body (5) and a grinding layerarranged thereon for the grinding machining of the at least oneworkpiece, and wherein the grinding layer comprises a plurality ofsurface segments (2, 3), wherein, in each case, a plurality of surfacesegments (2, 3) is provided both in the circumferential direction and inthe radial direction, characterized in that the grinding layer comprisesat least two different types of surface segments (2, 3) which havedifferent degrees of hardness.
 2. Grinding wheel (1) according to claim1, characterized in that at least a first group of harder surfacesegments (2) and a second group of softer surface segments (3) areprovided.
 3. Grinding wheel (1) according to claim 2, characterized inthat the harder surface segments (2) have a hardness that is at least 5%harder than the hardness of the softer surface segments (3), preferably10% to 20% harder than the hardness of the softer surface segments (3).4. Grinding wheel (1) according to claim 1, characterized in that atleast some of the surface segments (2, 3) are either circular orannular, or even hexagonal.
 5. Grinding wheel (1) according to claim 1,characterized in that at least some of the surface segments (2, 3) arequadrangular with straight and/or curved side edges.
 6. Grinding wheel(1) according to claim 1, characterized in that at least two adjacentsurface segments (2, 3) are separated from one another by a recessedarea (4), for example in the form of a groove.
 7. Grinding wheel (1)according to claim 6, characterized in that, viewed in the radialdirection, at least one recessed area (4) extends over the entire radialextension of the grinding wheel (1) and/or, viewed in the radialdirection, at least one recessed area (4) extends only over a partialarea of the radial extension of the grinding wheel (1).
 8. Grindingwheel (1) according to claim 6, characterized in that at least onerecessed area (4) extends radially or in the form of an involute. 9.Grinding wheel (1) according to claim 6, characterized in that at leastone recessed area (4), preferably each recessed area, is at leastpartially, preferably completely, filled with a filling material, suchas epoxy resin.
 10. Grinding wheel (1) according to claim 6,characterized in that at least one recessed area (4), preferably eachrecessed area, has a width of at least 1 mm, preferably 3 mm to 5 mm.11. Grinding wheel (1) according to claim 1, characterized in that atleast one harder surface segment (2) and at least one softer surfacesegment (3) are provided at each radial position when viewed in thecircumferential direction.
 12. Grinding wheel (1) according to claim 1,characterized in that the material thickness of the surface segments (2,3) is at least 3 mm, preferably 5 mm to 10 mm.
 13. Grinding wheel sethaving two grinding wheels (1) for the simultaneous material-removingmachining of both sides of at least two flat workpieces, characterizedin that at least one grinding wheel (1) is formed as a grinding wheel(1) according to claim 1, and preferably each of the two grinding wheels(1) is formed as a grinding wheel (1) according to claim 1.